Luminescence chronologies for coastal and marine sediments

More documents

Recommendations

Info

BOREAS Luminescence chronologies for coastal and marine sediments 515 Table 1 (continued) Ref No. Location Deposit types Age range Method Theme Reference Scotland 124 Orkney Isles aeolian1storm deposits LH OSL B, E Sommerville et al. E, F F (2003, 2007); Hall et al. (2006); Hansom & Hall (2008) 125 Shetland Isles sands LP IRSL, TL B Hall et al. (2002) Ireland 126 Northeast coast beach ridges1dunes H IRSL A Orford et al. (2003) 127 North coast coastal dunes H IRSL, OSL B, E Wilson et al. (2004) 128 Dingle Bay dune sands LH IRSL B Wintle et al. (1998) Wales 129 Aberffraw coastal dunes LH OSL B Bailey et al. (2001) Denmark 130 Skallingen Spit barrier-spit dunes LH OSL A, D, E Aagaard et al. (2007) 131 Wadden Sea tidal LH OSL H, J Madsen et al. (2007a, b) 132 Wadden Sea estuarine LH OSL A, H, J Madsen et al. (2005) 133 Jutland beach ridge1aeolian sand H OSL A, G Nielsen et al. (2006); Clemmensen et al. (2001a, 2006) B, E Murray & Clemmensen (2001) Strickertsson et al. (2001) 134 Skagerrak & Kattegat aeolian dunes LH OSL B, E Clemmensen & Murray (2006) 135 Gammelmark marine1aeolian LP OSL A, J Murray & Funder (2003) 136 Northwestern Jutland sand dunes LH OSL B, E Clemmensen et al. (2001b) Germany 137 North Sea tidal flat LH OSL A, H Mauz & Bungenstock (2007) Netherlands 138 Texel Island coastal dunes modern OSL G, H, J Ballarini et al. (2003, 2007); Van Heteren et al. (2006) G Lithuania 139 Baltic Sea marine sediments H IRSL G Bitinas et al. (2001) Oceans and Seas 140 Baltic Sea marine H OSL A Kortekaas et al. (2007) Arctic Sea deep-sea sediments LP-H OSL J Jakobsson et al. (2003) Arctic Sea marine LP-H IRSL J Berger (2006) Arctic Sea continental shelf H TL J Berger et al. (1984) North Pacific & Antarctic Oceans deep-sea sediments LP TL J Wintle & Huntley (1979a, b, 1980) 18 Northwest Australia deep-sea sediments LP-H OSL J Olley et al. (2004a) 86 Arabian Sea deep-sea sediments LP-H OSL J Stokes et al. (2003) exposed for a long duration (i.e. several days) to sunlight only (Singarayer et al. 2000). At the other end of Africa, along the southeastern African coast, Porat & Botha (2008) reported 57 ages from which they constructed a luminescence chronology for dune formation on the Maputaland coastal plain since marine isotope stage (MIS) 11. They used a MAAD TL procedure applied to potassium-rich feldspar grains to date beyond the effective limits of quartz OSL dating, and used a MAAD or SAAD (singlealiquot additive dose) IRSL method for the younger samples (o100 kyr). The oldest finite MAAD TL age obtained was 20313 kyr, similar to the oldest MAAD IRSL age of 21622 kyr. The advantage of TL over IRSL to extend the age range for potassium-rich feldspars was therefore not realized. Porat & Botha (2008) obtained ages for the Isipingo Formation, among others, which represents the
516 Zenobia Jacobs BOREAS 25° 155° 85° Greenland Iceland Asia North America Europe Japan 23.5° Africa South America 0° Australia 23.5° New Zealand 25° 155° 85° Fig. 1. Map of the world indicating all study locations where luminescence dating has been used to obtain chronologies for coastal or marine deposits, referred to in Table 1. Green squares, red stars and blue circles designate sites of TL, IRSL and OSL dating studies, respectively. aeolianites limited to the coastal barrier. They and Armitage et al. (2006) have shown that some, but not all, of the coastal aeolianite outcrops are associated with the MIS 5 sea-level maxima and interstadials. Porat & Botha’s age estimate of 20313 kyr is consistent with an earlier, MIS 7, sea-level highstand. Perhaps more surprising is the age estimate of 17924 kyr and a number of estimates around 65 kyr, which are associated with the transitions from MIS 7 to 6 and MIS 5 to 4, respectively. At both stages, the sea level was between 60 and 80 m lower than at present (e.g. Waelbroeck et al. 2002). The general pattern of ages, clustered around the last few interglacial sea-level maxima, is similar to what has been observed along the southern Cape coast of South Africa. A number of studies here have used SAR OSL methods to determine the timing of aeolianite and beachrock formation (e.g. Jacobs et al. 2003a, b, 2006; Bateman et al. 2004; Jacobs & Roberts in press) to assess the association between dune formation and changes in sea level. OSL ages obtained for beachrock at four locations along the coast at Nahoon in the Eastern Cape (Jacobs & Roberts in press), and at Sedgefield, Great Brak River and Agulhas, resulted in a combined weighted mean age estimate of 1283 kyr. Beachrock provides direct evidence of a former sea-level highstand, and these age estimates are consistent with independent estimates of 1261.7 kyr (based on a compilation of U-series ages) for the MIS 5e maximum (Waelbroeck et al. 2008). At these sites, aeolianites conformably overlie the beachrock and ages obtained for these aeolianites range between 115 and 125 kyr, which confirms their marine-aeolian association. In some sedimentary sequences, there are also additional aeolianite members with ages clustering around 90–100 kyr and 80 kyr. These are, in most cases, separated from the MIS 5e aeolianite by a protosol, indicating a period of quiescence followed by dune formation during the MIS 5c and 5a interstadials. This pattern is also reflected in the dating of dune sands trapped in the Pinnacle Point Cave 13B archaeological site (Marean et al. 2007). Here, two dune-forming events have been dated using OSL to 120 kyr and 90 kyr. The youngest of these is capped by a flowstone which has been dated by U-series to 90 kyr, verifying the veracity of the OSL ages and the general patterns observed along the coast. In detail, however, the pattern is complex, reflecting the observations of Porat & Botha (2008) along the Maputaland coast and other studies further afield in the Mediterranean and Australia. There is some evidence of pulses of dune formation during glacial periods. An example is the stack of aeolianite preserved along and below the cliff face at Blombos Cave, an important archaeological site near the town of Still Bay in South Africa. These aeolianites were dated to the transition between MIS 5 and 4 at 70 kyr, and their age equivalent is found as an uncemented dune sand overlying Middle Stone Age (MSA) archaeological layers inside the cave (Jacobs et al. 2003a, b, 2006). This 70 kyr dune-forming event has also been recorded in the Wilderness seaward dune cordon by Bateman et al. (2004). Further dune pulses during glacial periods are also recorded during MIS 3 at 392 kyr (Carr et al.
Page 1 and 2: Luminescence chronologies for coast
Page 3 and 4: 510 Zenobia Jacobs BOREAS This chan
Page 5 and 6: 512 Zenobia Jacobs BOREAS Table 1 (
Page 7: 514 Zenobia Jacobs BOREAS Table 1 (
Page 11 and 12: 518 Zenobia Jacobs BOREAS the SAR O
Page 13 and 14: 520 Zenobia Jacobs BOREAS (2004) us
Page 15 and 16: 522 Zenobia Jacobs BOREAS location
Page 17 and 18: 524 Zenobia Jacobs BOREAS MIS 6, in
Page 19 and 20: 526 Zenobia Jacobs BOREAS across th
Page 21 and 22: 528 Zenobia Jacobs BOREAS surface,
Page 23 and 24: 530 Zenobia Jacobs BOREAS Baretto,
Page 25 and 26: 532 Zenobia Jacobs BOREAS Huntley,
Page 27 and 28: 534 Zenobia Jacobs BOREAS Rhodes, E

Luminescence chronologies for coastal and marine sediments

Create successful ePaper yourself

Delete template?

Save as template?